It has to do with how people behave, as we see in the article here, and NZ gets much less international traffic than the US and the island take has some merit. Iceland had 10 cases, Madagaskar around 150. You could argue that South Korea is an island too since there probably is little exchange on land routes. Australia wishes to be a continent, but... okay, maybe it really doesn't really fit here.

Infections aren't spread homogeneously, so I believe behavior of people is the main factor. Too bad, because you cannot just blame all this on someone.

I think the causes of infections get misattributed just like the performance of economies to immediate government policies.